<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>05-id选择器</title>
    <style>
        #set-color {
            color: red;
        }

        .class-set-color {
            color: blue;
        }
        .class-set-size {
            font-size: 25px;
        }
    </style>
</head>
<body>
    <h1>id选择器</h1>

    <div id="set-color">这是 div 标签</div>
    <br>
    <div class="class-set-color class-set-size">这是 div 标签</div>
</body>
</html>